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Light Flashcards

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1
Q

What is the speed of visible light in a vacuum and air?

A

300 x 10^6 m/s

This speed is constant in a vacuum and approximately the same in air.

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2
Q

What type of wave is visible light?

A

Transverse wave

Transverse waves oscillate perpendicular to the direction of the wave’s travel.

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3
Q

What phenomenon allows us to see objects?

A

Reflection of visible light

Light reflects off objects and into our eyes, enabling vision.

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4
Q

What is diffuse reflection?

A

Reflection from an uneven surface that scatters light rays

Examples include paper or rough surfaces.

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5
Q

What happens when light reflects off a smooth shiny surface?

A

Only one light ray is reflected, creating a clear image

This is typical of reflections seen in mirrors.

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6
Q

What is the law of reflection?

A

Angle of incidence = angle of reflection

This law applies to all reflective surfaces.

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7
Q

What are virtual images?

A

Images formed when light rays appear to diverge from a point

The brain perceives the image where the rays converge, not where they reflect.

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8
Q

What causes refraction?

A

Change in speed of a wave as it passes from one medium to another

This change is due to differences in densities of the media.

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9
Q

What happens to a wave when it enters a denser medium?

A

It slows down and may change direction

The wave continues in the same direction if it hits the new medium head on.

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10
Q

Fill in the blank: The reflection of light from an uneven surface results in _______.

A

diffuse reflection

This type of reflection results in scattered light rays.

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11
Q

True or False: Virtual images can be seen at the actual point where light reflects.

A

False

Virtual images are perceived at a point where the light rays appear to diverge.

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12
Q

What can all waves do?

A

Be reflected and refracted.

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13
Q

What happens to a wave when it hits a denser medium head-on?

A

It slows down but carries on in the same direction.

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14
Q

What occurs when a wave meets a different medium at an angle?

A

Part of the wave hits the material first and slows down earlier, causing a bend and a change in direction.

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15
Q

When light enters a denser block, what direction does it bend?

A

Towards the normal.

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16
Q

What is the relationship between the angle of incidence and the angle of refraction when light enters a denser medium?

A

The angle of incidence is greater than the angle of refraction.

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17
Q

What changes occur to the wavelength and frequency of light when it enters a denser medium?

A

Wavelength gets shorter, frequency stays the same.

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18
Q

What happens to light when it exits a denser block into less dense air?

A

It speeds up and bends away from the normal.

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19
Q

What changes occur to the wavelength and frequency of light when it exits a denser medium?

A

Wavelength gets longer, frequency stays the same.

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20
Q

What is the refractive index?

A

A measure of how much light slows down when it enters a medium, also known as optical density.

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21
Q

What is the first step in investigating the refraction of light in a rectangular block?

A

Place a glass block on a piece of paper and trace around it.

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22
Q

What should be traced after shining a ray of light onto the glass block?

A

The angle of incidence and the emergent ray.

23
Q

What is observed as light passes into a denser medium of the block?

A

The ray bends towards the normal.

24
Q

What is observed as light exits into the less dense medium of air?

A

The ray bends away from the normal.

25
Q

What is the procedure for investigating the refraction of light in a semi-circular block?

A

Shine a ray box at the semi-circular block and measure the angle of incidence and refraction.

26
Q

What should be recorded in a table when investigating refraction in a semi-circular block?

A

The angles of incidence and refraction, along with sin(i) and sin(r).

27
Q

What do you plot to determine the refractive index from your results?

A

A graph of sin(i) against sin(r).

28
Q

How do you calculate the gradient of the line of best fit in the graph of sin(i) against sin(r)?

A

By doing rise / run.

29
Q

What happens to visible light when it enters a triangular prism?

A

It disperses into different colors, creating a rainbow effect

The colors are red, orange, yellow, green, blue, indigo, and violet (ROYGBIV), with red bending the least and violet the most.

30
Q

What is Snell’s law?

A

The refractive index (n) = sin(incident ray) / sin(refracted ray)

This law describes how light refracts when passing through different media.

31
Q

What is the refractive index of air or a vacuum?

A

1

Light travels fastest in air or a vacuum, which are assigned a refractive index of 1.

32
Q

What is the refractive index of glass?

A

Approximately 1.5

This means light slows down by a factor of 1.5 when passing through glass.

33
Q

What is the refractive index of water?

A

About 1.33

This indicates that light travels slower in water than in air.

34
Q

How can the refractive index of a material be determined?

A

By measuring angles of refraction for different angles of incidence and plotting sin(i) against sin(r)

The gradient of the graph gives the refractive index.

35
Q

What is the procedure to find the refractive index of glass using a glass block?

A
  1. Draw around a rectangular glass block on paper
  2. Direct a ray of light through it at an angle
  3. Trace the incident and emergent rays
  4. Measure angles of incidence and refraction
  5. Calculate the refractive index using sin(i)/sin(r)

This involves plotting a graph of sin(i) against sin(r) to find the gradient.

36
Q

What is the difference between real and apparent length in the context of refraction?

A

Real length is the actual distance, while apparent length is how far away an object seems due to refraction

For example, an object in water may appear further away than it actually is.

37
Q

True or False: The refractive index of any transparent material is always less than 1.

A

False

The refractive index is always greater than 1.

38
Q

Fill in the blank: The refractive index tells you how much a light wave ______ in a material.

A

slows down

For example, in glass with n = 1.5, light slows down to 200 x 10^6 m/s.

39
Q

What is total internal reflection?

A

Total internal reflection is when a light ray gets trapped in a material and reflects internally.

40
Q

When does total internal reflection occur?

A

Total internal reflection occurs when the angle of incidence is large enough that the light ray bends away from the normal and is reflected internally.

41
Q

What is the critical angle?

A

The critical angle is the angle at which any angle of incidence greater will cause the light ray to totally internally reflect.

42
Q

How can the critical angle be calculated?

A

The critical angle can be found using the formula sinC = 1 / refractive index.

43
Q

What is the relationship between refractive index and critical angle?

A

The higher the refractive index, the lower the critical angle.

44
Q

What is the critical angle for water?

A

In water, the critical angle is 49 degrees with a refractive index of 1.33.

45
Q

What is the critical angle for glass?

A

In glass, the critical angle is 42 degrees with a refractive index of 1.5.

46
Q

What are two applications of total internal reflection?

A

Total internal reflection is used in:
* Optical fibres
* Prisms

47
Q

How do optical fibres utilize total internal reflection?

A

Optical fibres are constructed so that the light is always hit at an angle greater than the critical angle, allowing light to be sent down the fibre.

48
Q

What role do prisms play in total internal reflection?

A

Prisms use total internal reflection to allow us to see objects that aren’t in our direct line of sight, such as in a periscope.

49
Q

At what angle does a ray of light enter a prism for total internal reflection?

A

The ray of light travels into a prism at 45 degrees.

50
Q

What happens to light in a prism during total internal reflection?

A

The light is internally reflected by 90 degrees, allowing it to travel parallel at a different height.

51
Q

True or False: The critical angle is the same for all materials.

A

False.

52
Q

What happens if the angle of incidence is less than the critical angle?

A

The light passes out of the block as usual

This describes the behavior of light when it strikes a boundary at an angle less than the critical angle.

53
Q

What occurs when the angle of incidence is equal to the critical angle?

A

The emerging ray comes out along the surface at 90 degrees to the normal

At this angle, the light ray refracts along the boundary between two media.

54
Q

What is the outcome when the angle of incidence is greater than the critical angle?

A

The light ray will totally internally reflect

This phenomenon occurs when light travels from a denser medium to a less dense medium.

Physics (12 decks)

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